The present invention relates to a method of synchronizing a measurement position of a scanning densitometer to photoelectrically scan small square printing surfaces containing respective colors called color patches, printed on an upper side blank portion etc. of a paper when a multi-color printing is implemented, and more particularly to a method to correct an asynchronous state of a measurement position produced by a difference between a scheduled color patch position and a color patch position determined depending upon a manner in which a paper is actually placed or mounted.
Scanning densitometers are used with a view to using a standard printing surface density as a reference to adjust a quantity of an ink supplied to a printing machine in accordance with a measured result of the printing surface density of a sample paper extracted during printing, thereby allowing the printing surface density to be in correspondence with the standard printing surface density. In operation, such densitometers photoelectrically scan a control strip constituted by connecting or joining color patches in each color serving as small square printing surfaces and printing them to an upper side blank portion etc. of a paper in the form of a ribbon. In such a scanning, photoelectric conversion is carried out every colors, e.g., black, red, blue and yellow etc., thus to take out outputs detected from color patches of corresponding colors as measured ouputs of respective colors.
In this case, since the printing surfaces are opposite to the ink supply roller and an adjustment of an ink supply quantity is made by a plurality of blades divided in the axial direction of the roller, color patches of respective colors are printed every divisional ranges divided in a transverse direction, i.e., in left and right directions with the color patches being connected or joined to constitute a series of control strips as a result of the fact that these color patches are connected or joined in the form of a ribbon. When a paper on which a control strip is printed is placed or mounted on a paper table to apply scanning to the paper along the control strip using a scanning densitometer, respective color patch positions of the control strip are shifted depending upon the mounting condition of the paper, so that they are not in correspondence with the scheduled positions of respective color patches, resulting in occurrence of asynchronism of measurement position due to the discrepancy between both positions. As a result, measured outputs do not correspond to outputs from only color patches of the scheduled colors, resulting in occurrence of a measurement error based thereon.
For the countermeasure therefor, there has been ordinarily employed in the art a method to artificially mark respective measurement designation positions in the vicinity of the control strip using a pen etc. to thereby determine the measurement positions of respective color patches to memorize these measurement positions at subsequent times to conduct only the measurement of the respective measurement positions, and a method to draw attention to the fact that color distinction, dimension in arrangement, form or configuration and the like are determined in advance to detect a color patch of a specified color by a change in measured density between adjacent color patches to conduct a measurement of color patches of respective colors with the color patch detected being as a standard of measurement.
However, with the method to designate respective measurement positions by marking a conduct a measurement on the basis of the memorization thereof, if shift of mounting condition of a paper, expansion and contraction of a paper, a deviation of printing site etc. occur, the measurement becomes inaccurate. On the other hand, with the method to detect a change in measured density between adjacent color patches to thereby determine the standard of measurement, when the form of the control strip is changed, there occurs the problem that this method cannot be applied as it is.